Evaluation of R-Factor for Outriggered Buildings

Abstract

Outrigger systems have been a prominent structural system for past thirty years in tall buildings. Even after that, not much data and design methodology is available for outrigger system. Outrigger reduces flexure demands at the base of core wall, thus reducing the length of core wall as well as increasing the lateral stiffness of the building. This paper presents calculation of response reduction factor for an outriggered building. Two 20 and 30 story prototype buildings, Tower A and Tower B having outriggers at top are designed and detailed as per Indian Standard 1893, 13920 and IS 16700. Detailed finite element models are prepared and non-linear static analysis (pushover) is performed to calculate the capacity of the structure. Influence of P-delta is also taken into account when calculating the R-factor.